1. Field of the Invention
The present invention relates to a fluid filter, and more specifically to a fluid filter which can suppress the close contact between folds of a filter material to prevent an increase in pressure loss and also can ensure the necessary filtration area to improve the filtration efficiency, even when outlet and inlet holes are arranged opposite to each other.
2. Description of the Related Art
As conventional oil filters for automatic transmissions, those having an upper case provided with an outlet hole, a lower case provided with an inlet hole, and a filter element held between the upper and lower cases are generally known (for example, see Related Art 1). The Related Art 1 discloses that outlet and inlet holes are arranged opposite to each other in the vertical direction. This layout of the inlet and outlet holes above involves the problem of reduction in filtration efficiency due to the bias generated in the flow of oil on a filtering surface, but is inevitably employed in some cases from the viewpoint of mounting requirements and the like.
Thus, it is conceivable to apply a filter element having a folded filter material to the oil filter disclosed in Related Art 1 to ensure a large filtration area within a limited space to enhance the filtration efficiency. In the case of this folded filter material 111, however, neighboring folds 111a may closely contact to each other to cause an increase in pressure loss, as shown in FIGS. 14(a) and 14(b). Especially, an outlet hole 102 and an inlet hole 104 are arranged opposite to each other in the vertical direction in the oil filter of Related Art 1, and thus a relatively high-pressure fluid would flow through a communication part 109 of a filtration chamber S which connects the outlet hole 102 and the inlet hole 104, thereby easily causing the close contact between the folds 111a of the filter material 111 in the communication part 109.
[Related Art 1] JP-A 2003-42272